1. Field of the Invention
The present invention relates to the field of communications systems. More specifically, the present invention relates to the networking of devices using phone lines.
2. Description of Related Art
The telephone lines that connect together and are wired into residences and businesses as a part of the telecommunications infrastructure (POTS--Plain Old Telephone System, PSTN--Public Switched Telephone Network) often come in one or more pairs, each pair consisting of two wires. Although most establishments have four wires, only two of those wires, known as "tip" and "ring" (collectively, "analog pair"), are utilized for voice and data communication. Voice and data communication carried over tip and ring utilize very low frequencies, typically below 3 KHz. When data is carried over the analog pair, a modem, which is typically a low-frequency device, is connected to a device such that the modem can convert binary information into low-frequency analog signals that can be transmitted over the analog pair.
On a single analog pair, currently there is no practice for simultaneously utilizing that pair for both voice (audio) and local area network (LAN) data communication, i.e., a person talking on the telephone line with a standard POTS telephone while a modem or other data device transmits information to other nodes (i.e., other modems) utilizing the same analog pair. The same pair cannot be used simultaneously for both voice and data on a traditional telephone line because the low-frequency signals which carry information originating from the modem or device would conflict and interfere with the voice and audio signals which travel over those same lines and at those same frequencies.
There is currently practice for utilizing the unused pairs in an establishment for performing networking or other data communication while analog pairs are being used for voice. The unused pairs do not substantially interfere with the voice communications ongoing on the active telephone line since the two lines are physically separate. However, this practice requires that the residence or other establishment have at least two pairs-one that is used for analog telephony, and one or more pairs dedicated to data communications. Some residences are only equipped with two pairs, one of which is required for voice telecommunications. In many instances, it is too cost prohibitive to install additional pairs that are devoted solely to data communications and networking. For example, to undertake 10 BaseT, CEBus.TM. (Consumer Electronics Bus, a trademark of the Electronics Industry Association), or Localtalk (a trademark of Apple Computer Corporation) communications, at least two additional pairs, which are quite expensive, are required. In those establishments which do have an additional pair, that pair is often used as a second phone line.
Another use of the existing analog pair for networking is ADSL (Asymmetric Digital Subscriber Line), which uses high frequencies to communicate across the PSTN (i.e. to dial outside the local area) for connecting, for example, to the Internet. ADSL however, cannot be used for local area networking on one analog pair since it is point-to-point (i.e. requiring a central master which is located distant from the local loop). ADSL requires significant changes to POTS wiring and the PSTN infrastructure. Since ADSL attempts to transmit high frequency signals over a long distance, a large amount of power is required to overcome parasitic losses. For local area networking, therefore, ADSL is not impractical, but inapplicable.
Thus, there is needed a practice for utilizing a single analog pair to carry out both voice communications and local area networking simultaneously without the signals interfering with or interrupting each other.